A seat heater (a heater for a seat) having a heater wire, which is a heating element, laid in, such as nonwoven fabric and urethane, has hitherto been used often for the heater-equipped seat of this type. The seat heater is accommodated in a seat, to thus heat a seating face.
FIG. 4 shows a related-art heater-equipped seat. As show in FIG. 4, a seat (not shown) usually has therein a heating element 1; a temperature detector 2 that is thermally coupled to the heating element 1 and that detects a temperature of the heating element 1; an operation unit 3, such as a switch by which a user turns on/off a heater (seat heater) and an adjustable controller by which the user varies a preset temperature; and a controller 4 that controls energization of the heating element 1 in accordance with a temperature detected by the temperature detector 2 and a state of the operation unit 3.
A thermistor is usually used for the temperature detector 2. A common control scheme is to utilize a phenomenon in which a resistance value of the thermistor changes according to a temperature of the heating element 1, and to control a temperature by detection of the phenomenon.
For instance, provided that the operation unit 3 is an adjustable controller for varying a preset temperature, the temperature of the heating element 1 is detected by the temperature detector 2, such as a thermistor. The controller 4 compares the thus-detected temperature with a temperature preset by the user through use of the adjustable controller. When the preset temperature has not yet been achieved, power is applied to the heating element 1. In contrast, when the preset temperature has already been achieved, application of power to the heating element 1 is suspended, thereby controlling the temperature.
Subsequently, application of power to the heating element 1 is resumed after elapse of a predetermined period of time since application of power was shut off or when the temperature of the heating element 1 has decreased to a predetermined temperature level. Temperature control is carried out by repetition of these operations.
The heater-equipped seat is set primarily in a driver's seat and a front passenger's seat in many cases. In particular, it is also assumed that no body is in the front passenger seat. If a operating unit for the front passenger seat is set in a heating position at this time, the heater will operate despite absence of a passenger after starting of the engine, which results in unwanted power consumption and deterioration of fuel efficiency.
Accordingly, various contrivances have hitherto been proposed as seating sensors for determining whether or not a passenger is in a seat. For instance, a known seat sensor has a plurality of cells disposed on a seat surface for detecting partial pressure from arrays, which are defined by rows set along a seat surface of a seat in its widthwise direction and columns set along the seat surface in its front-to-back direction, and determines whether or not a passenger is in a seat in accordance with the partial pressure detected by the cells (see; for instance, Patent Document 1).    Patent Document 1: JP-A-2002-87132